This invention is concerned with the removal of hydrogen sulfide from a mixture of gases.
In many industrial processes and in the oil production industry, concern over pollution has compelled the more complete removal of harmful and/or offensive components from effluent gas streams before release into the atmosphere. Also, many chemical processes demand gas streams of specific composition.
The problem is to separate gases from each other efficiently and economically and to dispose of any unwanted gas efficiently and economically.
A gas which is of particular concern as a pollutant is hydrogen sulfide. Hydrogen sulfide and other sulfur compounds are both offensive and harmful. Hydrogen sulfide, for example, can cause corrosion problems and is also toxic in concentrated amounts. Even in considerably less than toxic concentrations, hydrogen sulfide has an offensive odor.
The removal of hydrogen sulfide is complicated by the fact that it often occurs as a component in a mixture of gases. One frequently occurring gas mixture contains hydrogen sulfide and carbon dioxide along with perhaps other gases. Carbon dioxide is usually tolerated and not considered as a pollutant. Thus, it may be released into the atmosphere. There are many processes which will remove both hydrogen sulfide and carbon dioxide from gas streams and a few which may be made to preferentially remove hydrogen sulfide. Some of these processes use, in combination or alone, monoethanolamine and diethanolamine. Others use propylene carbonate, a combination of an alkali metal carbonate and an alkali metal arsenate, and others use a mixture of tetrahydrothiophene-1, 1-dioxide and alkanolamines. It is also known in the art to use an aqueous basic solution to remove both carbon dioxide and hydrogen sulfide since both gases increase in solubility in aqueous solutions as the pH of the solution rises.
Details of several prior art processes for treating mixtures of hydrogen sulfide and other gases are disclosed in the literature. See for example, "The Oil and Gas Journal", Aug. 14, 1967, p. 131; "The Oil and Gas Journal", June 3, 1968, p. 90; and "Chemical Engineering", May 15, 1972, p. 66.
These prior art processes have disadvantages such as requiring addition of fresh reagents as the active ingredients are used up in the process or regeneration of these active ingredients. Also, the pH of some systems is required to be maintained at a predetermined level requiring constant surveillance and manipulation. Also, many prior art processes do not adequately provide for disposal of the hydrogen sulfide after it is in solution.
Processes which provide for catalytic oxidation of hydrogen sulfide dissolved in an aqueous medium are disclosed in U.S. pat. No. 3,576,738 and applications Ser. No. 199,780 filed Nov. 17, 1971; Ser. No. 199,777 filed Nov. 17, 1971; and Ser. No. 199,779 filed Nov. 17, 1971. However, these processes are not directed to separating hydrogen sulfide from a mixture of gases but are concerned only with hydrogen sulfide already present in an aqueous solution.
The present invention overcomes many problems of the prior art by providing a process whereby hydrogen sulfide is at once preferentially absorbed from a gaseous mixture comprising hydrogen sulfide and carbon dioxide into an aqueous solution and then the hydrogen sulfide is catalytically oxidized to elemental sulfur while in solution.